This application relates to wireless communication systems and techniques.
Wireless communication systems use electromagnetic waves to communicate with wireless communication devices located within cells of coverage areas of the systems. A radio spectral range or band designated or allocated for a wireless communication service or a particular class of wireless services may be divided into different radio carrier frequencies for generating different communication frequency channels. The existing and developing specifications under IEEE 802.16x standards support wireless communications based on Orthogonal Frequency Division Multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA) are IEEE P802.16-REVd/D5-2004 and IEEE P802.16e/D5-2004.
FIG. 1 shows an exemplary wireless communication system 100 that uses communication channels at different frequencies under OFDM or OFDMA to provide wireless communication services and to implement the techniques described in this application. The system 100 may include a network of base stations (BSs) or base station transceivers 120 that are spatially distributed in a service area to form a radio access network for wireless subscriber or subscriber stations (SSs) 110. In some implementations, a base station 120 may be designed to have directional antennas and to produce two or more directional beams to further divide each cell into different sections. Base station controllers (BSCs) 130 are connected, usually with wires or cables, to BSs 120 and control the connected BSs 120. Each BSC 130 is usually connected to and controls two or more designated BSs 120.
The wireless system 100 may include a carrier packet network 140 that may be connected to one or more public switched telephone networks (PSTN) 150 and one or more packet data networks 160 (e.g., an IP network). A mobile switching center (MSC) 152 may be used as an interface between the BSCs 130 and the PSTN 101. A packet data serving node 142 may be used to provide an interface between the carrier packet network 140 and the packet data network 160. In addition, a carrier packet network manager 144 may be connected to the carrier packet network 140 to provide various network management functions, such as such as an AAA server for authentication, authorization, and accounting (AAA) functions.
Each subscriber station 110 may be a stationary or mobile wireless communication device. Examples of a stationary wireless device may include desktop computers and computer servers. Examples of a mobile wireless device may include mobile wireless phones, Personal Digital Assistants (PDAs), and mobile computers. A subscriber station 110 may be any communication device capable of wirelessly communicating with base stations 120.
In OFDM and OFDMA systems, it is desirable to control the transmitting power levels at different frequencies in order to achieve desired system operations, e.g., maintaining a certain level of the system performance and the quality of service.